The present invention relates generally to apparatus and methods for treatment of tissues using cooling and/or balloon inflation. In many embodiments, the invention provides systems, devices, and methods for cryogenically treating a patient's vasculature or other tissues by cooling the tissues to a temperature in a target temperature range, with cooling fluid pressure and/or the temperature control often being enhanced by measuring one or more characteristics of a cooling fluid flow control valve. Some embodiments may effect controlled inflation of tissue treating balloons with vaporizing and/or gaseous inflation fluids with or without therapeutic tissue cooling.
A number of percutaneous intravascular procedures have been developed for treating atherosclerotic disease in a patient's vasculature. The most successful of these treatments is percutaneous transluminal angioplasty (PTA). PTA employs a catheter having an expansible distal end, usually in the form of an inflatable balloon, to dilate a stenotic region in the vasculature to restore adequate blood flow beyond the stenosis. Other procedures for opening stenotic regions include directional atherectomy, rotational atherectomy, laser angioplasty, stents and the like. While these procedures, particularly PTA and stenting, have gained wide acceptance, they continue to suffer from the subsequent occurrence of restenosis.
Restenosis refers to the re-narrowing of an artery following an initially successful angioplasty or other primary treatment. Restenosis typically occurs within weeks or months of the primary procedure, and may affect up to 50% of all angioplasty patients to some extent. Restenosis results at least in part from smooth muscle cell proliferation in response to the injury caused by the primary treatment. This cell proliferation is referred to as “hyperplasia.” Blood vessels in which significant restenosis occurs will typically require further treatment.
A number of strategies have been proposed to treat hyperplasia and reduce restenosis. Previously proposed strategies include prolonged balloon inflation, treatment of the blood vessel with a heated balloon, treatment of the blood vessel with radiation, the administration of anti-thrombotic drugs following the primary treatment, stenting of the region following the primary treatment, the use of drug-eluting stents, and the like. While these proposals have enjoyed varying levels of success, these procedures have not proven to be entirely successful in avoiding all occurrences of restenosis and hyperplasia in all locations, and the costs for implementing many can be excessive for many patients.
It has recently been proposed to prevent or slow reclosure of a lesion following angioplasty in the coronary and/or peripheral vasculature by remodeling the lesion using a combination of dilation and cryogenic cooling. U.S. Pat. No. 6,300,029, the full disclosure of which is incorporated herein by reference, describes a structure and method for inhibiting restenosis using a cryogenically cooled balloon U.S. patent application Ser. No. 10/455,253, filed on Jun. 4, 2003, the full disclosure of which is also incorporated herein by reference, describes improved structures and methods for cryogenically cooling tissues in which a cooled balloon is controllably inflated to one or more intermediate pressures between a non-inflated configuration and a fully inflated, vessel dilating configuration. While these cooled therapies show great promise for endovascular use, the described structures and methods for carrying out endovascular cryogenic cooling would benefit from still further improvements. In particular, work in connection with the present invention indicates that accurate control over balloon inflation pressure, balloon temperature, and the process of going from an uninflated balloon configuration to an inflated cooling balloon configuration may not always provide a desired level of control over an inflation rate while making efficient use cryogenic cooling fluid.
For these reasons, it would be desirable to provide improved devices, systems, and methods for cryogenic cooling of blood vessels and other body lumens. In general, new and enhanced techniques for controlling pressures and temperatures of cryogenic treatments would be beneficial, especially if these improvements did not significantly increase the cost and/or complexity while providing more efficient use of cooling fluids. It would be particularly desirable if these improved devices, systems, and methods were capable of delivering treatment in a very controlled manner so as to limit injury of tissues during endovascular cryogenic balloon inflation.